Union of SQL tables, but only taking the first instance of an ID

I have three tables with identical columns that I need to union together into one table. Some IDs appear in more than one table, and I need to use the ID from the lowest numbered table first, and ignore that ID in any subsequent tables. Note that only the ID is the same, there aren't any duplicate rows between the tables.

So as an example, these three tables need to be transformed to the final table: